Heretofore, a fuel cell operating at high temperature, for example, a phosphoric acid fuel cell and a molten carbonate fuel cell, have been premised to be equipped in a large-scale power plant or the like. Accordingly, downsizing of a facility for the purpose of thermal independence thereof by thermal insulation and heat shielding has not been considered. However, a study has been made of downsizing and temperature lowering thereof, pertaining to a solid oxide fuel cell. And, mounting of the solid oxide fuel cell on a mobile object has become a possibility.
Although the study has been made pertaining to temperature lowering of the solid oxide fuel cell, operation temperature thereof has actually reached 500° C. or more. Therefore, in order to mount the solid oxide fuel cell on the mobile object such as a vehicle, a thermal insulating container for shielding heat transfer from the fuel cell concerned to other instruments comes to be necessary. As the thermal insulating container, there exists such for use in an electric furnace or the like, that is, such in which the electric furnace is surrounded by a ceramic thermal insulator with a thickness of several ten centimeters, and a metal container is provided on the periphery thereof. However, when the fuel cell contained in such a conventional thermal insulating container is mounted on the mobile object, a volume involved in the thermal insulation is too large. Therefore, there has been proposed a method of housing the solid oxide fuel cell in a vacuum thermal insulating container made of stainless steel (refer to Japanese Patent Laid-Open Publication No. H08-138721 (published in 1996)).